In recent years, electronic devices have been introduced for controlling various electrical equipment in a vehicle such as an automobile. In an electric power steering apparatus as an example of an electrical equipment into which an electronic device is incorporated, there is provided a motor drive unit in a enclosure accommodating an electric motor for steering an automobile and the electronic device is mounted on the motor drive unit. The electronic device is incorporated as a power module into the motor drive unit.
The power module is constituted as a so-called semiconductor module on which a power element such as a field effect transistor (FET) or an insulated gate bipolar transistor (IGBT) suitable for controlling an electrical equipment driven with a relatively large current, such as an electric power steering apparatus. Such a type of power module is also called “in-vehicle module”, because it is mounted on a vehicle.
As an example of such a type of semiconductor module, a semiconductor module illustrated in FIG. 17 (see PTL 1) is known. FIG. 17 is a cross-sectional view schematically illustrating an example of a semiconductor module in the related art.
The semiconductor module 100 illustrated in FIG. 17 includes a metal substrate 101, a resin 102 formed on a bottom flat surface of a recessed portion of the substrate 101, and plural copper foils (wiring patterns) 103a, 103b, 103c, and 103d formed on the resin 102. Grooves 109 are formed between the copper foil 103a and the copper foil 103d and between the copper foil 103c and the copper foil 103d. Thermal buffer plates 104a and 104b are formed on the copper foils 103a and 103b out of the copper foils 103a, 103b, 103c, and 103d, respectively, and IGBTs 105a and 105b are formed on the thermal buffer plates 104a and 104b, respectively. Each of the IGBTs 105a and 105b is a bare-chip IGBT (bare-chip transistor).
The emitter of the IGBT 105a and the copper foil 103b are jointed to each other by a wiring 106a constituted of a wire, and the emitter of the IGBT 105b and the copper foil 103c are similarly jointed to each other by a wiring 106b constituted of a wire.
In addition, the resin 102, the copper foils 103a, 103b, and 103c, the thermal buffer plates 104a and 104b, the IGBTs 105a and 105b, and the wirings 106a and 106b are sealed by a gel 107. In addition, a cover 108 covering the recessed portion of the substrate 101 is fixed to the upper portion of the substrate 101.
As another example of the semiconductor module in the related art, a semiconductor module illustrated in FIG. 18 (see PTL 2) is also known. FIG. 18 is a cross-sectional view illustrating another example of the semiconductor module in the related art.
In the semiconductor module 200 illustrated in FIG. 18, an insulating substrate 202 is jointed by soldering onto a heat-dissipating base plate 201 made of aluminum or the like.
A collector electrode 205 of an IGBT 203 is jointed by soldering onto a metal film formed on the insulating substrate 202.
On the other hand, in the semiconductor module 200, the interconnection member 206 is a flat plate member made of a highly-conductive metal material such as copper and includes an electrode-facing portion 206A facing an emitter electrode 204 of the IGBT 203, a rising portion 206B bent upward from the electrode-facing portion 206A to rise, and a lead-out portion 206C extending from the rising portion 206B. The lead-out portion 206C is connected to an external connection terminal (not illustrated). Then, the lead-out portion 206C is provided with a wavelike bent portion 206D. The bent portion 206D serves as a stress-reducing portion for absorbing a thermal expansion difference between the interconnection member 206 and the heat-dissipating base plate 201 and reducing the thermal stress.
The electrode-facing portion 206A of the interconnection member 206 and the emitter electrode 204 of the IGBT 203 are jointed to each other with a conductive resin 207. Since the conductive resin 207 has an elastic modulus lower than that of a jointing conductive material such as a solder, it is possible to effectively reduce a thermal stress.
Moreover, as another example of the semiconductor module in the related art, a semiconductor module illustrated in FIG. 19 (see PTL 3) is also known. FIG. 19 is a plan view schematically illustrating another example of the semiconductor module in the related art.
In the semiconductor module 300 illustrated in FIG. 19, plural conductive pads 301 and 302 are formed on a substrate (not illustrated). A MOS chip 303 is jointed by soldering onto one conductive pad 301 out of the plural conductive pads 301 and 302. Plural source electrodes 305 and a single gate electrode 304 are formed on the top surface of the MOS chip 303, and a drain electrode (not illustrated) is formed on the bottom surface of the MOS chip 203.
Then, the source electrodes 305 of the MOS chip 303 and the other conductive pad 302 out of the plural conductive pads 301 and 302 formed on the substrate are connected to each other via a lead 310. The lead 310 is formed by punching and bending, that is, by press forming, a metal plate. The lead 310 includes a source electrode-jointing portion 311 having a rectangular flat plate shape and extending in the X direction and the Y direction (horizontal direction) illustrated in FIG. 19, an electrode-jointing portion 312 having a plate shape and extending in the X direction and the Y direction, and a coupling portion 313 being inclined in the Z direction (up-down direction) and coupling the source electrode-jointing portion 311 and the electrode-jointing portion 312 to each other. Here, the source electrode-jointing portion 311 is jointed by soldering to the source electrodes 305 of the MOS chip 303, and the electrode-jointing portion 312 is jointed by soldering to the other conductive pad 302 out of the plural conductive pads 301 and 302 on the substrate. There is provided a pair of the other conductive pads 302 and the electrode-jointing portion 312 has a shape of a pair of leg portions jointed to the pair of conductive pads 302.
The width a of the source electrode-jointing portion 311 in the X direction is equal to or greater than the width b of the plural source electrodes 305 in the X direction.
Accordingly, it is possible to prevent a positional shift relative to the source electrode 305 due to non-uniform solder wetting on the source electrode 305 and a reflow of the solder.